Light-emitting devices have been researched and developed more and more extensively these days to find applications in various types of displays including electro-luminescence displays (ELD), plasma displays (PDP) and field emission displays (FED), among other things, and eventually realize displays with even higher image quality and even higher efficiency. Taking an ELD and an FED as examples, Non-Patent Document No. 1 outlines an ELD as follows. One example is an ELD having a basic structure of applying an electric field to a fluorescent material, which is a light-emitting layer, via an insulating layer. Known ELDs with such a structure are classified into organic dispersion types and thin film types. An organic dispersion type has a structure in which ZnS particles, doped with Cu, for example, are dispersed in an organic substance, an insulating layer is deposited thereon, and the assembly is sandwiched between top and bottom electrodes. The dopant forms a pn junction in the fluorescent particles. When an electric field is applied, electrons emitted by a high electric field generated on the junction planes are accelerated and then recombined with holes to emit light. Another example has a structure in which a fluorescent thin film, made of Mn-doped ZnS, for example, which is a light-emitting layer, is arranged between electrodes with insulating layers interposed. Since the insulating layers are interposed, a high electric field can be applied to the light-emitting layer, and the emitted electrons accelerated by the electric field excite the emission centers to emit light. FED, on the other hand, includes an electron emission device and a fluorescent material that faces the device in a vacuum container. The FED accelerates electrons, emitted into a vacuum by the electron emission device, and bombards the fluorescent layer with the electrons, thereby emitting light.
In each of these devices, the emission of electrons triggers the emission of light, and therefore, it is important to develop a technique to emit electrons at a low voltage and with high efficiency. As such a technique, emission of electrons by inverting the polarization of ferroelectrics has attracted a lot of attention lately. For example, Non-Patent Document No. 2 proposes that PZT ceramic 101, having a plane electrode 102 on one side and a lattice electrode 103 on the other side, be arranged so as to face a platinum electrode 104 with a grid electrode 105 interposed between them in a vacuum container 106 and that a pulse voltage be applied between the electrodes to emit electrons as shown in FIG. 12, in which the reference numeral 107 denotes a gas outlet port. According to this proposal, the pressure in the container is 1.33 Pa (10−2 Torr), and discharge does not occur at the atmospheric pressure.
Such a method of emitting light from a fluorescent layer by accelerating electrons, emitted by inverting polarization of ferroelectrics, in a vacuum container and, and a display using such an emission technique are also disclosed in Patent Documents Nos. 1 and 2. However, the basic arrangement is almost the same except that light is emitted from a fluorescent layer by replacing the platinum electrode of Non-Patent Document No. 2 with an electrode including the fluorescent layer.
On the other hand, a light-emitting device that uses electrons emitted by inverting the polarization of ferroelectrics in a non-vacuum is disclosed as an electric emission surface light source device in Patent Document No. 3, for example. As shown in FIG. 13, the device includes a bottom electrode 112, a ferroelectric thin film 111, a top electrode 113, a carrier multiplication layer 118, an emission layer 114, and transparent electrode 116, which are stacked in this order on a substrate 115, and the top electrode has an opening 117. By inverting a voltage pulse applied between the bottom and top electrodes, electrons are emitted into the carrier multiplication layer through the opening of the top electrode, accelerated by the positive voltage applied to the transparent electrode, reach the emission layer while being multiplied, and emit light. Patent Document No. 3 also discloses that the carrier multiplication layer is made of a semiconductor, of which the dielectric constant is relatively low and which has such a band gap as not to absorb the emission produced by the emission layer at a particular wavelength. This device may be regarded as a type of ELD. Meanwhile, Patent Document No. 4 discloses an arrangement in which an emission layer of a fluorescent substance that has been formed by a sputtering process is sandwiched between two insulating layers and a pulse electric field is applied thereto and in which one of the two insulating layers is a ferroelectric thin film.
The applicant of the present patent application also proposed an inexpensive flat light-emitting device with a simple configuration in Patent Document No. 5. In that light-emitting device, a voltage is applied to two electrodes that are arranged in contact with the surface of a porous emitter to cause electrical discharge. And fluorescent particles in the porous emitter are excited with an ultraviolet ray produced as a result of this electrical discharge, thereby emitting light. The applicant of the present patent application further disclosed a plasma display panel in Patent Document No. 6, in which barriers that define an electrical discharge space have different heights in column and row directions in order to avoid accidental electrical discharge and to increase the luminance.                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 07-064490        Patent Document No. 2: U.S. Pat. No. 5,453,661        Patent Document No. 3: Japanese Patent Application Laid-Open Publication No. 06-283269        Patent Document No. 4: Japanese Patent Application Laid-Open Publication No. 08-083686        Patent Document No. 5: Japanese Patent Application Laid-Open Publication No. 2004-200143        Patent Document No. 6: Japanese Patent Application Laid-Open Publication No. 2005-011743        Non-Patent Document No. 1: Shoichi Matsumoto, et al, “Electronic Display”, Ohmsha Ltd., Jul. 7, 1995, pp. 147-151.        Non-Patent Document No. 2: Junichi Asano, et al, “Field-Excited Electron Emission from Ferroelectric Ceramic in Vacuum”, Japanese Journal of Applied Physics, Vol. 31, Part 1, pp. 3098-3101, September 1992        